A set up assembly is commonly used to secure a workpiece holder, such as a vise, to a machine tool table within the range of a machine tool, thereby facilitating a machining operation upon a workpiece mounted on the workpiece holder. For high precision machining of critically dimensioned workpieces, or parts, it is absolutely necessary that the set up assembly provide accurate and repeatable positioning of the workpiece with respect to both the machine tool table and the machine tool. For the purposes of this application, the term "machining" is meant to encompass, for instance, milling, grinding, drilling, boring, etc.
During machining, it is often necessary to hold the workpiece at an angle with respect to the machine tool, so that an accurate angled cut can be made. For this reason, a conventional set up assembly includes a pair of hinged set up plates. A bottom plate is attachable to the machine tool table and a top plate supports the workpiece holder and is hinged to the bottom plate. The top plate, sometimes referred to as a sine plate, is supported at a desired angle by a gauge block.
The top and bottom plates are hingedly connected by a first roll that is fixedly secured to the top plate along the axis of connection. A second roll is mounted to the raisable side of the top sine plate, and is spaced from, and parallel to, the first roll. When the top plate is in an unraised position, the rolls support the top plate in a horizontal plane, with the rolls being spaced a fixed distance apart. When the top plate is hingedly raised about the first roll, the gauge block is situated between the bottom plate and the second roll, supporting the top plate in a raised position. Because the fixed distance between the rolls is known and the height of the gauge block is also known, an angle of inclination between the plates can be readily determined and easily repeated in subsequent operations. With the bottom plate secured to a machine tool table, a workpiece holder secured to the top plate, and a workpiece mounted to the workpiece holder, the workpiece can be held at a desired angle with respect to the table during a machining operation simply by raising the unhinged end of the top plate and supporting it at the desired angle with a gauge block.
In the manufacture of parts that only require one machining step to be performed, sufficient precision can be achieved by carefully following a prescribed set up procedure. In this procedure, the workpiece must be mounted to the vise, the vise secured to the top plate, and the bottom plate secured to the machine tool table. After hinged raising of the top plate, the roll must also be further tightened to the top plate in order to secure the assembly. When it is necessary to machine a large number of similar parts, the above described set up procedure must be accurately repeated for each of the parts. Although required in order to ensure precision, the repetitive performance of this same set up procedure constitutes a significant loss of operator time. This repetition can also cause operator fatigue or boredom, and result in error. Furthermore, the tightening of the top plate to the roll introduces some inaccuracy along the axis of connection.
Some parts require a particular machining operation to be performed upon opposite sides, or symmetrically with respect to a vertical axis that bisects the part. For these parts, the set up assembly, and in particular the bottom plate, must be disconnected and turned around on the machine tool table in order to position the workpiece at the required angle for completion of the second machining operation. In the mass production of parts of the this type, a great deal of time is lost in tearing down and connecting the set up assembly in a turned around position. Again, tediousness associated with accurately repositioning of the bottom plate for successive parts can increase the probability of operator error.
Another disadvantage of conventional set up assemblies relates to the manufacturing of parts that require multiple machining operations at multiple stations, or the measuring of the part on the fixture with a microscope or comparator in order to ensure accuracy. In moving a part to another station, it is required either that the fixture and part be removed from the set up assembly and mounted accurately at the remote station, or that the entire assembly, i.e., both plates, the fixture and the workpiece, be moved and accurately mounted at the remote station. In both cases, time is lost in the repetitive movement and remounting at subsequent work stations of partial or entire assemblies. Additionally, in order to promote assembly line production of the parts along the multiple stations, costs would increase because it would be necessary to use multiple set up assemblies, with one entire assembly per station. In short, the versatility of set up assemblies has not kept pace with the practicalities of mass manufacture of parts which require multiple machining operations, or one machining or measuring step at a remote work station.
Some versatility in machining operations can be achieved with a compound set up assembly, which utilizes several gauge blocks to hingedly raise a mounted workpiece about either one of, or both of, two perpendicular axes of connection. Robertson et al. U.S. Pat. No. 3,075,291 discloses a set up assembly that enables pivotal movement of a top plate with respect to the bottom plate along either of two perpendicular axes. While assemblies of this type do provide some increased versatility, they do not solve the aforementioned problems with respect to the mass production of parts requiring multiple machining operations, or machining upon opposite sides of a part. Moreover, compound set up assemblies of the type disclosed in Robertson typically fail to adequately hold a workpiece in a stable position during machining.
In another form of compound set up assembly, multiple pairs of set up plates are stacked to the desired height. If four pairs of set up plates are used, the uppermost plate may be raised about any one of up to four separate, vertically displaced axes. However, stacking of this type is costly, due to the number of plates typically required. Additionally, these stacked assemblies suffer from the same disadvantages mentioned previously, that of requiring an inordinate amount of set up time.
Thus, while present set up assemblies may provide a degree of accuracy in holding a workpiece at a desired position with respect to a machine tool table during a machining operation, their versatility is extremely limited, particularly in the mass production of articles that require multiple machining operations.
It is an object of this invention to provide a versatile set up assembly that accommodates accurate positioning of a workpiece with respect to a machine tool table when the workpiece requires multiple machining or measuring operations to be performed at multiple stations.
It is another object of this invention to provide a versatile set up assembly that achieves accurate and repeatable positioning of a workpiece with respect to a machine tool, but requires significantly less set up time.
It is yet another object of this invention to provide a set up assembly that facilitates the machining of opposite sides of a workpiece.
It is still another object of this invention to provide a set up or work station assembly that facilitates the mass production of parts.